Group B Public Water Systems - Flooding


Image of flooding around house

Floods are the most common and widespread of all natural disasters, except fire, according to the Federal Emergency Management Agency. Most communities have experienced some degree of flooding following heavy rain or spring and winter thaws.

Floods pose a particular threat to drinking water systems because floodwaters often carry biological and chemical contaminants that can make consumers sick. If source water or any part of the water distribution system flood, these contaminants can end up in consumers' drinking water.

How Floods Contaminate Drinking Water

Source: Contaminants can enter the water supply if the wellhead or the areas immediately around the wellhead flood. If your system uses surface water, the elevated turbidity can make it impossible to effectively treat the water.

Distribution systems: Contaminants can enter the water distribution system if a significant loss of pressure occurs when all or part of the service area floods.

During a flood, you may have to ask consumers to conserve water. That request can confuse consumers when flooding or heavy rains make it look like there's water everywhere.

Even if the water system isn't contaminated, you may experience taste or odor problems.

What to do When the Weather Forecast Predicts Flooding in Your Area

If you routinely disinfect your water system with chlorine, increase the chlorine level. This will not ensure your drinking water will remain safe, but it will make it easier to monitor chlorine residuals in your water system. A drop in the chlorine residual may indicate contaminated water entered your water system.

What to do if Your Well or Distribution System Floods

NOTE: Exercise extreme caution any time an electric power supply component is under or near floodwater.

  • If your wellhead is flooded, or if the water system loses pressure while flooded, advise residents to bring their drinking water to a rolling boil for one minute to kill disease-causing bacteria and parasites. Do this even if you chlorinate your water system because your treatment may not be effective against contaminated floodwaters.
  • We created a wellhead flooding (Word) document for you to use to notify your customers.
  • Collect at least two coliform samples from your system.
  • Review the results of the sampling and advise your customers about the status of their drinking water supply.

For a list of certified labs, visit the state Department of Ecology. Under "Location," select your state, city, and county. Scroll down and click on "Show results." Click on the name of a lab to see the tests it performs. Call the lab to make sure it's accredited to analyze for coliform bacteria.

Communicate With Your Customers

  • Your customers' perception of risk during a flood may be high. They need timely and accurate information about the quality of their drinking water.
  • Not all customers experience the same flooding conditions. Some may feel a direct threat from floodwaters, while others do not. It's important to know your water quality and communicate to all customers.
  • Be conservative and informative, not sorry later on! Make sure your customers have the information they need to make good decisions about their drinking water.

Where to Go for Help

Our regional office staff or your local health jurisdiction can assist you during a flood emergency.

You can also call your emergency management agency. Contact information is online at the Washington Military Department's Emergency Management Division